1. Field of the Invention
The present invention relates to a heat- and abrasion-resistant aluminum alloy and a spring retainer and a valve lifter formed from the alloy.
2. Description of the Related Art
In recent years, various aluminum alloys with improved heat resistance and mechanical strength have been developed. A known method of producing a heat resistant aluminum alloy employs the technique of forming quenched powder followed by extrusion and so forth for the purpose of improving heat resistance. Although this kind of alloy offers high heat resistance, this does not always offer good abrasion resistance. In sliding characteristics, the level of this alloy is very similar to conventional aluminum alloys at the present stage. The plausible surface hardening methods, such as plating, involve complex processing, and hence result in increased production costs.
An aluminum alloy with relatively high abrasion resistance and mechanical strength is disclosed, for example, in JP-A-2-285043 entitled "An Al--Si alloy powder forging material with extremely low thermal expansion coefficient". The aluminum alloy contains 35 to 45% by weight of primary crystal Si with a particle size of 2 to 15 .mu.m and 5 to 20% by volume of aluminum oxide with a particle size of 5 to 20 .mu.m.
However, because aluminum oxide particles are included in its texture which comprises the matrix of the order of several tens of .mu.m and Si crystals of a relatively large particle size, around 10 .mu.m, the known alloy, though its abrasion resitance may be improved, has a drawback in that the strain is likely to concentrate due to the influence of the Si crystals and aluminum oxide particles present therein. Further, the known material may have some other defects due to the non-homogeneity of the powder deformation that may occur during the forming and hardening process thereof, leading to decreased toughness and strength after fatigue.